Rocket fuels



United States Patent 3,153,901 ROCKET FUELS Ellis B. Rifkin, Oak Park, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Apr. 3, 1958, Ser. No. 726,048 2 Claims. (Cl. oil-35.4)

This invention relates to high energy fuels and more particularly to additives which improve the combustion properties thereof.

An object of this invention is to provide new compositions of matter. A further object is to provide new fuels suitable for use in jet propulsion engines such as rocket engines. A further object includes provision of methods for utilizing such fuels. Still another object is the improvement of conventional rocket fuels.

It has now been found that hydrocarbon-soluble cyclopentadienyl manganese tricarbonyl compounds greatly improve the combustion properties of hydrocarbon jet propulsion fuels when added to such fuels in amount so that the concentration of the hydrocarbon-soluble cyclopentadienyl manganese tricarbonyl is at least 7 percent of the total weight of the composition.

These new additives improve the combustion properties of hydrocarbon jet propulsion fuels in several ways. When such fuels containing the additives of this invention are used with oxidants in systems with an external source of ignition, it is found that ignition is more positive than that for the same systems without the present additives. Important aspects of this more positive ignition are that ignition delay is decreased, smoother combustion is achieved and danger of explosion during starting is minimized.

Furthermore, under many conditions many of the additives of this invention render the hydrocarbon fuels hypergolic when contacted with jet propulsion oxidants. By this is meant that many of the fuel compositions of this invention are spontaneously inflammable when contacted with certain oxidizing agents such as nitric acid and the like. Hyperglocity is, of course, very important in jet and rocket propulsion as it results in simplified motors, eliminates the ignition system entirely, saves weight and provides for more reliable operation.

One of the chief advantages achieved by use of this invention is the reduction of combustion instability in rocket motors. This instability, often called screaming or screeching, frequently results in poor operation and occasionally actual destruction of the rocket motor while in operation. It is known that use of .hypergolic mixtures has a beneficial effect in reducing the magnitude of the pressure pulsations which cause screaming, and this invention therefore provides a means of obtaining longer life and smoother operation of rocket motors.

The improved hydrocarbon fuel compositions of this invention also possess other properties which are important in a successful jet propulsion fuel. Thus, they are of relatively high density, high boiling point, low freezing point and may be handled readily under normal precautions. Moreover, they are capable of being stored for long periods of time without losing their desirable combustion properties.

The additives of this invention are hydrocarbon-soluble cyclopentadienyl manganese tricarbonyl compounds. They have the basic structure 3,153,91 Patented Oct. 27, 1964 eral, compounds employed in this invention contain from 5 to 9 carbon atoms in the cyclopentadiene portion of the molecule.

For best results cyclopentadienyl manganese tricarbonyl compounds which are liquid at ordinary temperatures are used. These possess the advantages of being miscible in all proportions with the hydrocarbon fuels and of being more readily metered and blended than are the solid materials. Examples of liquid additives include methylcyclopentadienyl manganese tricarbonyl, ethylcyclopentadienyl manganese tricarbonyl, dimethylcyclopentadienyl manganese tricarbonyl, etc. Liquid alkyl cyclopentadienyl manganese tricarbonyl, particularly methylcyclopentadienyl manganese tricarbonyl, are preferred.

On the other hand, satisfactory results are obtained when the hydrocarbon-soluble cyclopentadienyl manganese tricarbonyl is a solid at ordinary temperature. Examples of such compounds are cyclopentadienyl manganese tricarbonyl itself, indenyl manganese tricarbonyl, benzoylcyclopentadienyl manganese tricarbonyl, etc.

Further examples of compounds both liquid and solid within the scope of this invention are butylcyclopentadienyl manganese tricarbonyl, propylcyclopentadienyl manganese tricarbonyl, diethylcyclopentadienyl manganese tricarbonyl, phenylcyclopentadienyl manganese tricarbonyl, acetylcyclopentadienyl manganese tricarbonyl, and the like. The additives of this invention and methods for their preparation are described in detail in US. Patents 2,818,416 and 2,818,417.

The fuel to which the manganese compound is added can be any hydrocarbon or mixtures of hydrocarbonsaliphatic, aromatic or naphthenic. This includes gasoline, kerosene, the jet fuels commonly designated as JP-l, JP-3, JP4, JP5, etc. and hydrocarbon distillate fuels in general as well as pure hydrocarbons such as benzene, hexane, octane, decane and the like. The aliphatic constituents may be either saturated or unsaturated. The jet fuels, because of reliability, good basic combustion properties, desirable physical properties, etc., constitute preferred hydrocarbon fuels of this invention.

These jet fuels are principally hydrocarbon fuels heavier than gasoline. In other words, they are distilled liquid hydrocarbon fuels having a higher end point than gasoline. They are generally composed of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbon fractions. The end point of preferable jet fuels is at least 435 F. and preferably greater than 480 F.

Typical jet fuels improved according to this invention include JP-3, a mixture of about 70 percent gasoline and 30 percent light distillate having a percent evaporated point of 470 F.; JP-4, a mixture of about 65 percent gasoline and 35 percent light distillate, a fuel especially designed for high altitude performance; JP5, an especially fractionated kerosene; low freezing point kerosene, etc;

When employing my new mixtures as fuels any oxidant used for the combustion of fuels in jet propulsion may be used. Examples are liquid oxygen, nitric acid, white fuming nitric acid, red fuming nitric acid, mixed nitric and sulfuric acids, fluorine, nitrogen tetroxide, hydrogen peroxide, potassium perchlorate, perchloryl fluoride, and the like. For ease in handling and operation the liquid oxidants are preferred. Particularly preferred are the nitrogen-containing liquid oxidants as best results are achieved with these.

In general, the benefits of this invention are realized as long as the hydrocarbon fuel contains at least 7 percent of the cyclopentadienyl manganese tricarbonyl additive. It is found that the exact degree of improvement achieved varies with several factors such as the nature of the additive, the type of fuel, the temperature and pressure of combustion, the degree of atomization of the fuel and,

indeed, the identity of the oxidant. For example, it is found that while all the additives of this invention improve the combustion characteristics of the hydrocarbon fuels not all of them are hypergolic. Of those which are hypergolic they are not all hypergolic at all concentrations, particularly the lower concentrations. Also the manifestation of hypergolicity varies according to other factors such as temperature and pressure. In general, compositions wherein the concentration of cyclopentadienyl manganese tricarbonyl is at least percent tend to be hypergolic. Ordinarily little is gained by increasing the concentration of cyclopentadienyl manganese tricarbonyl above 75 percent. Compositions consisting of hydrocarbon fuel containing 15 to 75 percent of a fuelsoluble cyclopentadienyl manganese tricarbonyl are therefore preferred.

The compositions of this invention are clear, lightcolored, low freezing, high boiling, mobile liquids which are stable in the presence of air at ordinary temperature. Among the above properties one of the most important is freezing point. A successful jet propulsion fuel must be very low freezing to function properly under winter conditions. The fuel compositions of this invention possess satisfactorily low freezing point. For example, a mixture of 15 percent methylcyclopentadienyl manganese tricarbony land 85 percent JP-4 has a freezing point of 22 C. The freezing point of a percent methylcyclopentadienyl manganese tricarbonyl-80 percent JP-4 mixture is -15 C., and that of a -75 percent mixture is 14 C.

The fuel compositions of this invention can readily be prepared by conventional blending procedures. Generally, the fuel-soluble cyclopentadienyl manganese tricarbonyl is added to an excess of the hydrocarbon fuel. Due to the favorable solubility of the additives, blending is accomplished by mere physical agitation of the mixtures. In the case of liquid additives, this blending is almost instantaneous. Even in the case of the solid materials, blending is usually accomplished within a very short period of time.

Due to the favorable solubility characteristics of my additives, I normally carry out blending at room temperature. A closed system is preferably used to minimize fire hazard and toxicity problems.

The following examples illustrate typical compositions of this invention.

Example I To 93 parts of benzene are added 7 parts of cyclopentadienyl manganese tricarbonyl. The resultant clear, mobile liquid has combustion properties superior to those of benzene when ignited with a liquid oxidant.

Example I] A mixture is prepared consisting of 75 parts of ethylcyclopentadienyl manganese tricarbonyl and 25 parts of kerosene. This clear liquid material is hypergolic with red fuming nitric acid.

Example 111 A mixture consisting of 10 parts by weight of isopropylmethylcyclopentadienyl manganese tricarbonyl and 90 parts by weight of distillate hydrocarbon fuel having an end point of 550 F. is prepared by slowly adding isopropylrnethylcyclopentadienyl manganese tricarbonyl to the fuel with agitation. The resulting clear, light-colored liquid possesses improved combustion properties when atomixed with hydrogen peroxide, liquid oxygen and fluorine as compared with the fuel not containing the additive.

Example IV A mixture is made up of 15 parts methylcyclopentadienyl manganese tricarbonyl and 85 parts of JP-4. This hypergolic mixture possesses improved combustion properties when contacted with an oxidant such as White fuming nitric acid.

4x Example V A hypergolic mixture of 50 percent ethylcyclopentadienyl manganese tricarbonyl and 50 percent n-hexane is prepared according to the procedure of Example I. It is found to possess improved combustion properties as compared with n-hexane not containing the additive.

Further examples of compositions within the scope of this invention and their utiliy are exemplified as follows:

A 10 percent solution of methylcyclopentadienyl manganese tricarbonyl in JP-4 jet fuel, when contacted with its own volume of red fuming nitric acid at room temperature, caused a vigorous reaction with the evolution of red fumes. The same reaction was observed when this hydrocarbon composition was contacted with three times its volume of red fuming nitric acid. When solutions of 15, 20 and 25 percent methylcyclopentadienyl manganese tricarbonyl in JP-4 were contacted with red fuming nitric acid, rapid and vigorous ignition was spontaneously achieved. In some instances this hypergolic phenomenon was sustained for several seconds. In other instances, the hypergolic reaction was so vigorous that all the fuel was used up essentially simultaneously.

The hydrocarbon fuel-cyclopentadienyl manganese tricarbonyl compositions of this invention retain their valuable properties after storage for considerable lengths of time. Thus, 20 and 25 percent solutions of methylcyclopentadienyl manganese tricarbonyl in IP-4 were stored in the dark in the presence of air at room temperature for two weeks. At the end of this time they were tested and found to be still hypergolic. These and other mixtures have been stored upwards of 50 days under these conditions without loss of hypergolic activity.

The new fuels of this invention can be used in many types of rocket propulsion systems. In one such system, the fuel and the oxidant are stored in separate tanks under an atmosphere of inert gas. This gas may be nitrogen, helium, argon, etc. The inert gas is also used to pressure feed the fuel and oxidant into the combus' tion chamber. To acomplish this, the inert gas is stored at high pressure in a tank which is connected by lines to the fuel and oxidant tanks. This line is equipped with a valve to isolate the fuel and oxidant tanks from the compressed gas tank. Connecting the fuel tank with the combustion chamber is a line for feeding fuel to the combustion chamber. A similar line connects the oxidant tank with the combustion chamber. Each of these lines has an automatically controlled valve to regulate rate of feed of fuel and oxidant to the combustion chamber. The inlets into the combustion chamber are arranged so that the two incoming streams contact each other forcibly, thereby achieving very intimate mixing.

In a typical operation according to this invention, the oxidant tank is loaded with red fuming nitric acid and the fuel tank is filled with a hypergolic mixture of 25 percent methylcyclopentadienyl manganese tricarbonyl in n-octane. The inert gas tank is filled with argon to a pressure of 400 pounds per square inch. The lines connecting the argon tank with the oxidant and fuel tanks are opened. Combustion is started by opening the valves in the lines between the fuel and oxidant tanks and the combustion chamber. The valves are adjusted to provide a flow of 10 gallons per second of fuel and 30 gallons per second of oxidant to the combustion chamber. The fuel and oxidant react violently and almost instantaneously upon contacting each other in the combustion chamber. A large volume of combustion gases is produced. This gas escapes through the orifice at the rear of the combustion chamber and thereby provlides jet propulsion which moves the vehicle.

For fuels which are not hypergolic, the same type of system can be used, except that a spark plug or other mechanical ignition system is provided in the combustion chamber.

I claim:

1. The method of achieving jet propulsion which 00mprises introducing into a combustion chamber (a) an improved hydrocarbon jet propulsion fuel containing from 7 to about 75 percent of a fuel soluble cyclopentadienyl manganese tricarbonyl compound, and (b) an oxidant selected from the class consisting of liquid oxygen, nitric acid, white fuming nitric acid, red fuming nitric acid, mixed nitric and sulfuric acids, fluorine, nitrogen tetroxide, hydrogen peroxide, potassium perchlorate and perchloryl fluoride, whereby combustion takes place upon reaction of said fuel and said oxidant, and ejecting from the combustion chamber the gaseous products of said combustive reaction.

2. The method of achieving jet propulsion which comprises introducing into a combustion chamber (a) a fuel consisting essentially of a hydrocarbon jet propulsion fuel containing a fuel-soluble cyclopentadienyl manganese tricarbonyl compound and (b) an oxidant selected from the class consisting of liquid oxygen, nitric acid, white-fuming nitric acid, red-fuming nitric acid, mixed nitric and sulfuric acids, fluorine, nitrogen tetroxide, hydrogen peroxide, potassium perchlorate and perchloryl fluoride, said cyclopentadienyl manganese tricarbonyl compound being present in an amount sufficient to render the reaction between said fuel and said oxidant hypergolic, but in a concentration of not more than about percent, whereby upon contact of said fuel and said oxidant combustion takes place, and ejecting from the combustion chamber the gaseous product of said combustive reaction.

References Cited in the file of this patent UNITED STATES PATENTS 2,771,739 Malina et a1 Nov. 27, 1956 2,818,416 Brown et al Dec. 31, 1957 2,818,417 Brown et a1 Dec. 31, 1957 2,839,552 Shapiro et a1 June 17, 1958 OTHER REFERENCES Journal of the American Rocket Society, No. 72, December 1947, pages 12 and 32. 

1. THE METHOD OF ACHIEVING JET PROPULSION WHICH COMPRISES INTRODUCING INTO A COMBUSTION CHAMBER (A) AN IMPROVED HYDROCARBON JET PROPULSION FUEL CONTAINING FROM 7 TO ABOUT 75 PERCENT OF A FUEL SOLUBLE CYCLOPENTADIENYL MANGANESE TRICARBONYL COMPOUND, AND (B) AS OXIDANT SELECTED FROM THE CLASS CONSISTING OF LIQUID OXYGEN, NITRIC ACID, WHITE FUMING NITRIC ACID, RED FUMING NITRIC ACID, MIXED NITRIC AND SULFURIC ACIDS, FLUORINE, NITROGEN TETROXIDE, HYDROGEN PEROXIDE, POTASSIUM PERCHLORATE AND PERCHLORYL FLUORIDE, WHEREBY COMBUSTION TAKES PLACE UPON REACTION OF SAID FUEL AND SAID OXIDANT, AND EJECTING FROM THE COMBUSTION CHAMBER THE GASEOUS PRODUCTS OF SAID COMBUSTIVE REACTION. 